carb conversion?

[pfo186]

hello all,
i have a 77' and was wondering how easy it was to convert to the vm34 slide carbs? I've read some threads on here how it's possible to get the jetting to work, but i was curious if the newer carbs bolt right on or if there is some fabrication involved?

my carbs are pretty trashed and they seem to be very temperamental in the first place.

I appreciate the insight.

PF

P.S. they make these conversion kits readily available for honda CB's, why not for the xs?

 

[Scorpio1963]

If Im not mistaken you have to use different carb holders intakes.Thats all I know.I have been reading about trying the same thing.I have noticed the jetting is way big on these carbs so Im sure they`ll have to be rejetted.

 

[Robsteeler66]

Are the stock carbs tunable? I've heard good things about Mikuni carbs, why do so many xs400's have problems with them?

 

[Scorpio1963]

tunable to the extent they can be rejetted and the slide needles adjusted.
The main problem of these carbs is they are finicky.Like any carb they have be spotless clean.The only thing I like is the simpicity to work on.
As per good things about them it depends on the model,they`re different versions of these carbs.They were used on alot of different bikes not just yamahas

 

[pfo186]

i have my carbs running decent, but still finicky. it took forever to get it running good, i finally ended up with a bigger main on my right carb than my left and it runs good. right side was running leaner for some reason. the air screw tips broke off and wedged in carbs (common problem for these) i drilled them out and they work ok even though that orphice is slightly bigger now. instead of spending good money on old used finicky BS34's i thought it would be better to use the modern vm34's if possible.

appreciate any insight from someone who has successfully done this.
thanks

 

[Robsteeler66]

Has anyone tried the Keihn Cv carbs on an xs400? They also have a great reputation.

 

[HoughMade]

...why do so many xs400's have problems with them?

Because:

A) They're not clean, no matter what you think;
B) People have modified them in an effort to make 650 power from a 400 and screwed them up,
C) People have not followed the advise all over XS400.com to get them clean, put on an external fuel filter, and richen the idle mixture,
D) The valves, points, timing or other parts are not in good repair, or
E) All of the above.

 

[Robsteeler66]

Good to know. I will add enriching the idle mixture to my mental list.

 

[pfo186]

Because:

A) They're not clean, no matter what you think;
B) People have modified them in an effort to make 650 power from a 400 and screwed them up,
C) People have not followed the advise all over XS400.com to get them clean, put on an external fuel filter, and richen the idle mixture,
D) The valves, points, timing or other parts are not in good repair, or
E) All of the above.

thanks for the info.

I have the carbs clean, and i richened up the idle mixture according to other threads on here. have not done an external fuel filter though. valves, points and timing are good. i'm just worried they will never run 100% correct becuase i had to drill out the idle mixture screw tip and that orphace is bigger now.

was just wondering if it would be a better choice to buy the new vm34's instead of investing in old used BS34's.

bike runs decent when it's 80 degrees or above outside, when it's cooler out it starts to get a bit lean as the idle spikes when it engine is hot. no blue pipe and plug chop looked good.

 

[HoughMade]

I'm sure the VM34 have been and can be adapted to run very well. My point is simply that the simpler, cheaper and easier route is to get the BS34s to run right, and that can be done.

 

[WelderDave]

So I’m in the same boat, drilled out the broken piece with a 1/16 as there was no other way to get it out, tried for 2 hours no luck with anything.

Thoughts on different carbs? Or will it be fine? Should I drill out the other one to match? Should I go down a pilot jet now?

 

[WelderDave]

I’ve to much time and money invested now it’s rediculous and I’m getting pissed off that the previous owner was a POS and f@&$ed everything up. I’ve been running into problem after problem. Already spent $100 in jets for these carbs and now I had to drill out that mix screw. I can’t invest more money, and it’s nearly done. I have to get the carbs up and running so I can try and run them as best I can to just make it work decent.

Do they make oversized mixture screws for this or anything I can do?

 

[xschris]

If you have to drill them out you must use micro size drill bits and keep the hole to the original size hole. Any larger are it will never tune correctly.

 

[xschris]

http://www.xs400.com/threads/fuel-mixture-screw-assembly-help.11329/#post-117312

 

[WelderDave]

To late, already did it. No money left to buy a carb. What’s next? How can I make it work?

 

[xschris]

I will never work right again. I made the same mistake about 12 yrs ago had to buy another set .

 

[WelderDave]

Ugh, I’ve spent $2000 on this project already in expected and unexpected things.

 

[WelderDave]

Alright, so I've seen the video on youtube of the mikesxs performance carb kits. The price is a little steep, but I'm going to switch to them. I've originally been trying to sell my second car to save the cash, but I'm gonna use it for those. I'll be selling my used BS34's. the left cylinder carb has the 1/16's hole i drilled in it, but that will be disclosed beforehand, figure someone will be looking to use the drilled one for parts. second one is good though. I've also got to go through all the extra parts on my bike to try and sell them. I'll make a list of stuff and pst it up on here and the faecbook group, if nothing then ill post on ebay.